JPH0136337B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotational position signal generator, and more particularly to a small, inexpensive, and highly accurate position signal generator.

For example, in a magnetic disk storage device, 1
To determine the starting position in the track, press 1.
A rotational position signal (index signal) is required for each rotation, but this signal has extremely small fluctuations in the rotational position where the signal is generated, even if there are changes in the environment such as temperature and humidity or changes in the power supply voltage. For example, an accuracy of 0.2° or less per rotation is required.

In order to generate such high-precision rotational position signals, conventional methods have involved attaching iron pieces to the rotor of a magnetic disk drive motor or providing recesses in the iron rotor, and detecting changes in magnetic resistance caused by these using a proximity switch. The method was used. Although this method has a simple structure, it has the disadvantage that the proximity switch is very expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide a small-sized rotational position signal generating device that can obtain a highly accurate position signal at low cost without using the proximity switch, and can house the entire device in a motor.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows a rotating magnet type motor to which the present invention is applied, where 1 is a rotor, 2 is a rotating magnet fixed to this, and
3 is an armature core, 4 is an armature winding, an index magnet 5 is attached to the rotor 1, and a bias magnet 6 is attached to the iron core 3, facing the index magnet 5.
and a magnetic sensor 7 located in front of the magnet 6. The magnetic sensor 7 is a combination of an analog output sensor element such as a Hall element and a high gain amplifier such as an OP amplifier or voltage comparator.
A hole in which the amplifier and a Hall element are integrally formed.
An IC (Hall switch) may also be used.

When the bias magnet 6 faces the index magnet 5, it has a polarity opposite to that of the index magnet 5 so as to reverse the polarity of the magnetic field acting on the Hall element of the magnetic sensor 7. A simple ferrite magnet is used, and a rare earth cobalt magnet or the like having a large coercive force is used as the index magnet 5. Inside the motor, there is a rotating magnet 2.
Since there is a magnetic field caused by the magnetic field caused by the armature winding 4 and a magnetic field caused by the armature winding 4, the bias magnet 6 is determined to have enough strength to stabilize the output polarity of the Hall element against these magnetic fields.

Figure 2 shows a circuit diagram of the magnetic sensor 7 using a Hall element, where 8 is a DC power supply terminal, 9 is an index signal output terminal, 10 is a Hall element, and 11 is an OP.
The amplifier 12 is a feedback resistor for preventing chattering. When the motor is operated, a signal containing a pulse signal p having a rotation period To of the motor is outputted to the output terminals a and b of the Hall element 10, as shown in FIG. 3a. In the figure, the part m is the output due to the magnetic field of the bias magnet 6, and the part n is the output due to the magnetic field whose polarity is reversed by the index magnet 5. The latter output is waveform-shaped by the OP amplifier 11 and becomes a rectangular wave pulse p1. Line 1 indicates the zero line of the combined magnetic field of both magnets 5 and 6.

The width of the pulse signal p1 changes depending on the waveform of the pulse signal p and the strength of the combined magnetic field of both the magnets 5 and 6. The pulse width of the signal p decreases almost linearly as the temperature rises, while the residual magnetism of both magnets 5 and 6 has a negative temperature coefficient, and the temperature coefficient of the residual magnetism of magnet 6 is equal to that of magnet 5. Since it is larger than that, the zero line l2 at high temperature is different from the zero line l1 at low temperature.
becomes lower. Therefore, the rising time T1 and the falling time T2 of the pulse signal p1 vary depending on the temperature, and as the temperature rises, T1 advances by t1 and T2 lags by t2. According to experiments, t1
is 3.9 μs when the magnetic disk rotation speed is 3600 rpm.
(Figure 4), and when converted into a rotation angle, it was 0.084°. In other words, even if a Hall element is used, the angular accuracy is
It is possible to obtain a highly accurate rotational position signal that fully satisfies the required accuracy of 0.2 degrees. In the above experiment, the magnetic sensor 7 was attached to the space between the poles for measurement.

As described above, according to the present invention, by using a magnetic sensor equipped with a Hall element and a high gain amplifier, a highly accurate rotational position signal that can be used as an index signal for a magnetic disk can be obtained at low cost. In addition, all the parts for generating the signal can be directly incorporated into the motor, which has the effect of simplifying the design of the device.

[Brief explanation of drawings]

The drawings are partial elevational views of one embodiment of the present invention, FIG. 2 is a circuit diagram of a magnetic sensor, FIGS. 3 a and b are a Hall element output waveform diagram and a magnetic sensor output waveform diagram, respectively, and FIG. 4 is a magnetic sensor output waveform diagram. FIG. 3 is a diagram showing a variation characteristic due to temperature at the time of the rise of an output pulse. 1... Motor rotor, 3, 4... Motor stator, 5... Index magnet, 6... Bias magnet, 7... Magnetic sensor, 10... Hall element, 11... High gain amplifier .

Claims (1)

[Claims] 1. A bias magnet attached to one of two members that rotate relative to each other, and a bias magnet attached at a predetermined angular position of the other member to locally reverse the polarity of the magnetic field. A rotational position signal comprising an indexing magnet with a large magnetic force, a Hall element attached to the one member to detect the reversal, and a magnetic sensor including an amplifier that shapes and amplifies the detection signal of the Hall element and outputs a rotational position signal. Generator. 2. The rotational position signal generating device according to claim 1, wherein the index magnet is attached to the motor rotor, and the magnetic sensor and bias magnet are attached to the motor stator. 3. The rotational position signal generating device according to claim 1 or 2, wherein the index magnet is a rare earth cobalt magnet, and the bias magnet is a ferrite magnet.